In conventional cardiopulmonary bypass systems, blood is taken from the patient's right atrium and passed through an oxygenator and pumped back into the aorta, thus bypassing the patient's heart and lungs. A blood pump, filters and reservoirs are all included in the system. Large volume venous reservoirs are placed in the blood flow circuit between the right atrium and the inlet to conventional roller or centrifugal cardiopulmonary bypass pumps. While these systems have been commonly employed for years, they are causing problems to patients with regard to brain oxygenation. There are two reasons for this: (1) the roller and centrifugal pumps cannot produce physiologic pulsatile flow, necessary for the brain and other vital organs, and (2) the large venous reservoirs cause hemodilution, thereby diminishing the oxygen carrying capacity per unit of blood. The use of large venous reservoirs increases the cost of the system as well as traumatizing the blood through induction of a large air-blood interface and exposure of blood to large non-endothelial surfaces. Also, increased priming volume, usually a crystalloid solution, is needed when large reservoirs are employed, resulting in dilution and diminished oxygen carrying capacity of the patient's blood.